1. Field of the Invention
This invention relates to an image forming apparatus such as a printer, a facsimile, or a copier using electrophotography for forming a toner image on a record material of paper, etc., and more particularly to an art of forming a toner image (patch image) of a predetermined pattern on the surface of a toner image support to adjust the density (and gradation) of a toner image and measuring the density with a density sensor (patch sensor).
2. Description of the Related Art
In an image forming apparatus in a related art, a patch image is formed on the surface of a belt-like image support for supporting a toner image on the surface and is detected with a patch sensor placed facing a placing part on a roller for stretching the belt-like image support. (Refer to Japanese Patent Publication JP-A-2002-214854.)
According to the configuration, it can be expected that it will be made possible to detect the patch image on the surface of the belt-like image support with good accuracy in the placing part on the roller where a flutter does not occur on the belt.
On the function of the patch sensor, the distance and the angle relative to a measured object largely affect the sensing performance of the patch sensor. Particularly, if the measured object is a curved surface, the angle accuracy needs to be managed strictly.
The image forming apparatus in the related art described above is not provided with an adjustment mechanism of the angle which the patch sensor forms with the measured object (patch image on the image support), and the position of the patch sensor is guaranteed by the parts accuracy.
Thus, in the image forming apparatus in the related art, variations in patch sensor attachment angle easily occur, resulting in large density variations after sensing; this is a problem.